Resistor



L. TASSARA May 2, 1961 RESISTOR Filed Sept. 15, 1958 INVENT OR lu/e/ 7/26 4 n t Z twa v Pat fit'Ofi c 2,982,933 7 REstsT oR' H Luigi Tassara, Via Olmetto 3,'Milau, Italy Filed Sept. 15,1958, Ser. No. 761,034 l Claims. (Cl. ass-4 72) This invention relates to film-type electrical resistors and especially to those having low resistance.

In making resistors by depositing a resistive film on a cylindrical insulator as disclosed, for example, in my co-pending U.S. patent application Ser. No. 761,061, entitled Apparatus for Applying Metallic Film to Electrical Components and the Like, it is sometimes desirable to provide resistors .havingvery low values of resistance but which have sufiicient size and mass to provide good heat dissipation. Such resistors could be made by simply depositing a very thick film of resistive material, but this would greatly increase the time required to form the resistor and would render it uneconomical for mass production.

According to the present invention these disadvantages are overcome by providing properly shaped end terminals. These end terminals, instead of being in the form of short, conductive caps, as has been the usual practice heretofore, are, according to the present invention, triangular in shape, and the terminals are so located with respect to each other as to leave a relatively narrow, helical gap which is bridged by the resistive film. Because of the low resistance of the end terminals, most of the voltage drop takes place across the gap, which means that the efiective length of the resistive film is rather short (equal to the width of the gap), while the width of the film is relatively great (equal to the length of the spiral gap). The resistance of such a resistor is quite low, with values down to the order of one-half ohm being easily obtainable, and yet, because of the large surface area of the resistor and the intimate contact between the resistive film in the gap, where heat is produced, and the heat-dissipating conductive terminals, overall heat dissipation is quite high.

The invention will be further described in connection with the drawing in which the only figure shows the novel resistor and a developed view of the conductive terminal and resistive coating on the cylindrical surface of the resistor.

The resistor consists of a cylindrical ceramic rod 11 having recesses (not visible) in each end, or extending all the way through, into which terminal wires 12 and 13 may be inserted. These wires are held in place by any convenient means, such as by filling up the recesses with solder 14.

Conductive end terminals 16 and 17 cover the ends of cylinder 11 and electrically connect with the terminal wires 12 and 13, respectively, for example, through conductive caps 32 and 3 3. These terminals are triangular in shape, as is better shown in the developed view to the right of the resistor.

One way in which terminals 16 and 17 can be formed is by coating the entire rod 11, except for a spiral gap 18 and another gap 19, with silver paste and baking the coated rod to make the paste adhere firmly. The gaps could be formed by masking the rod or by removing some of the silver by grinding it off after it has been baked. The essential thing is that a complete break be formed in the silver so that there will be no short-circuit :has been found to be very suitable.

to the resistance of the device. this is but a small portion of the total, developed length 2,982,933 Patented May 2, 1961 as a spiral.

Over the entire cylindrical surface is deposited a resistive film 21. Such a film may be formed in any convenient way, but the apparatus disclosed in my co-pending application Ser. No. 761,061, referred to hereinabove,

Most of the resistive film 21 will fall upon the conductive terminals 16 and '17 and will be of no effect, so far as serving as a resistor is concerned, because it will be short-circuited by the contiguous conductive terminals. Only that part of film 21 falling on gaps 18 and 19 will be effective in adding In the embodiment shown of film 21, which is 1rd, d being the diameter of the ceramic rod 11.

If it is desired to control the resistance precisely, enough resistive material 21 should be deposited to reduce the total resistance between wires 13 and 14 to a value that is below the desired amount. Then grooves may be ground through the resistive material 21 in the gaps, as indicated between the dashed lines 22. Such grinding has the least eifect when perpendicular to the gap. The closer the grinding gets to being parallel to the gap, the greater will be its effect on increasing the resistance.

While gap 19 is shown as being about the same width as gap 18, there is no need to have it so. The resistance between wires 13 and 14 is primarily determined by the resistance of the material in gaps 18 and 19, and in the embodiment shown, these gap resistances are in parallel with each other. Of course, one of the gap resistances may be made much higher than the other by making one gap much wider than the other or by cutting down the width of the current path across one gap. This is the purpose of grinding a slot between lines 22. Such a slot could also be formed in gap 19 or the resistance of gap 19 could be raised to an infinite value by making a longitudinal cut through it.

While triangular-shaped end terminals 16 and 17 are perhaps the easiest to make and while they lead to the lowest values of resistance, the amount of silver paste can be reduced by applying it only along the proximal edges 23 and 24 of the gap 18.

While this invention has been discussed in terms of a particular embodiment, those skilled in the art will at once appreciate the fact that modifications therein may readily be made and that the true scope of the invention is defined by the following claims.

What is claimed is:

1. A resistor comprising a cylindrical insulator body, a conductive connecting means mounted upon each of the two ends of said body, a pair of conductive terminals, one of said terminals being joined to said connecting means at each end of said body and being formed intimately about said body, each of said terminals extending in opposite directions towards each other along the length of said body to make considerable portions of them longitudinally coextensive with each other, said terminals being spaced apart from each other to provide gaps between their adjacent edges, said gaps being relatively narrow in comparison to their length and at least one of said gaps being disposed along a helical path on said body, and a resistive film covering said terminals and said body to bridge said gaps and overlap said adjacent edges to make contact with both of said terminals to provide a resistance between said connecting means which is a function of the distance across said gaps.

2. A resistor as set forth in claim 1 wherein each of said terminals is angularly shaped when in a flat condition to permit a pair of adjacent edges of said terminals to be disposed in a helical path when said terminals are 2,9 2,933 1 I V p i intimately formed .about said body to provide a helical gap between said edges. 1 v

v 3. A resistor comprising a cylindrical insulating body, a conductive connecting means mounted upon each of the'two ends of said body, a pair of conductivelend'ter- .minals which are shaped as similar triangles inJtheir fiat form, one of said terminals being joined to'sa'id connecting means at each end of said body and 'being'formed tween said connectingmeans which is a function of the .distance across said gaps intimately about said body and spaced from each other a to form gaps therebetween, each of said terminals 'ex tending in opposite directions towardseach other an formed intimately about said bodyto provide 'a pair of substantially helical edges separated by a helical gap,

anda resistive film covering said terminals and said body to bridge said gaps and overlap said edges to make contact with both of said terminals to provide a resistance be- 4. A resistor as set forth in claim 3 wherein said terminals are shaped as right triangles when they are in a flat condition and when formed about said cylindrical body they form two gaps between said terminals, one of said gaps extending longitudinally along said body and the other of said gaps being helica'lvin shape, said gaps inter secting each other to provide complete separation of said end terminals, and said resistive film covers substantially all of the cylindrical surface of said body and overlaps said gaps to make contact with both of said end terminals.

References Cited in the file ofthis patent UNITED STATES PATENTS 2,052,533 Pender Aug. 25, 1936 2,188,667 Stoekle Jan. 30, 1940 v2,337,202 v Jones Dec. 21, 1943 Framburg May 9, 1944 

